In an arrangement, discussed for example by D. Sievenpiper, L. Zhang, R. F. J. Broas, N. G. Alexopolous and E. Yablonovitch in “High-Impedance Electromagnetic Surfaces with a Forbidden Frequency Band,” IEEE Trans. On Microwave Theory and Technology, Vol. 47, No. 11, November 1999, a high impedance surface has been created using a structure in the form if a close-packed periodic array of square-topped “thumb tack” or mushroom-shaped metal elements connected a ground plane surface by means of vias. A representation of the structure of Sievenpiper et al. is shown in FIG. 1. This structure is intended for use with signals of microwave frequency, usually defined to lie in the region of the electromagnetic spectrum between infra-red and radio waves and so of frequency in the range of 1 to 300 GHz typically. The structure shown in FIG. 1 is therefore typically of a scale that allows for fabrication using printed circuit techniques.
If the structure described by Sievenpiper et al. were to be scaled up in size to be suitable for use with signals in the range of 100 MHz to 1 GHz, the result would be a bulky and heavy structure.